1. Field of the Invention
The present invention pertains generally to dynamic magnetic information storage or retrieval and more particularly to systems and methods used in controlling the electronic circuitry through which the information signal is processed.
2. Description of Related Art
Modern computers perform a variety of tasks. Obviously, for example, computers perform computations. Most recently, computers have also gained popularity as communication devices, providing E-mail and internet access capabilities. No less important, however, is a computer's capability of storing and managing large amounts of data, such as on a magnetic disk, a CD ROM, or a magnetic tape.
Mass data storage is a crucial aspect of modern computer usage. For example, a bank typically stores large volumes of data, including customer records, financial market data, and internal business records, in large interconnected computer systems. Current data is generally stored in primary storage media, such as memory arrays, magnetic hard disks or optical disks, for rapid access. In many organizations, however, this data is regularly archived (or "backed-up") on archive media, such as alternate magnetic or optical disks or for larger volumes on magnetic tape, to preserve the data for future access. Preferably, the current data is copied from the primary storage media in the computer system to the archive media. The archive media is then stored in a safe location, preferably off-site, to protect the archived data from destruction. In this manner, the existence of the current data on both the primary storage media and the archive media minimizes the risk of losing the data. For example, a fire at the bank could destroy the copy of the data in the primary storage media, but the archived data copy would still be intact. The bank could then load the archived data into the computer system to recover most of the necessary data. In the recovery process, data recorded on the tape is typically read from the tape and re-recorded on a primary storage medium.
Data recorded onto a magnetic tape is typically organized into a specific tape format. Tape formats can vary according to tape types (e.g., 1/2 inch, 1/4 inch, and 8 mm magnetic tape). For example, on a 1/2 inch reel tape, data bytes are typically recorded in parallel data records onto the nine track tape. The number of bytes in a physical data record vary between one and 65,535 bytes. The available tape formats for 1/2 inch reel tapes generally include 800 BPI (Bytes Per Inch), 1,600 BPI, and 6,250 BPI. Actual storage capacity is a function of the recording format and the length of the tape reel. In contrast, on a 1/2 inch cartridge tape, data is recorded serially onto the 1/2 inch cartridge tape. The data records are recorded on cartridge tape tracks in a serpentine manner. As one track is completed, the recording drive switches to the next track and begins writing in the opposite direction, eliminating the wasted motion of rewinding. The number of bytes per data record is determined by the physical data record size specified by the recording device. Accordingly, the tape format in which data is to be recorded onto or read from the tape can affect, among other characteristics, storage capacity, transfer rate, data organization, and the mechanical movement of the tape during recording.
As the amount of data residing in the computer system increases, however, the time and computer resources required to archive the data also increase. In many circumstances, for example, back-up procedures are performed after normal work hours to minimize the impact on the performance of the computer system during the normal business day. In a typical configuration, data stored on one or more magnetic hard disks is read into a host computer system and organized (i.e., formatted) to be compatible with a particular tape data format. The host system then records the formatted data onto the magnetic tape. This continuous involvement of the host system in the back-up process consumes substantial host system computing cycles and decreases the host system's performance in other processes. Furthermore, to process the data at rates sufficient to keep up with the streaming speed of the tape, the involvement of the host system, including communication to and from the host system, becomes a bottleneck. Consequently, need exists for a system and method to minimize the host system involvement in the tape backup and recovery processes, particularly during the transfer of the data to and from the source storage medium to the tape.